This invention relates to buffer stops for use on the permanent tracks of railways and is particularly concerned with buffer stops of the kind which include means for imparting a frictional braking force to a train which has made an impact with the buffer stop.
It is an object of the invention to provide a simple and inexpensive buffer stop of the aforesaid kind which, on impact of a train with the buffer stop, will provide a frictional braking force which progressively increases as the train is gradually brought to a standstill, thereby substantially reducing risk of any sudden jerk on initial impact with the buffer stop.
According to the invention, the improved buffer stop comprises a buffer structure including a pair of transversely spaced side walls each adapted to extend lengthwise of and adjacent to one rail of the permanent track of a railway and having spaced from its, lowermost edge a plurality of slots mutually spaced along the length of the side wall, each slot of one side wall extending substantially parallel to the adjacent rail and being directly opposite to and of substantially the same length as a substantially identical slot in the other side wall, and a plurality of pairs of transversely spaced two-part clamps for detachably securing the side walls of the buffer structure to the rails of the permanent track at spaced positions along the lengths of the side walls, each two-part clamp of each pair comprising a pair of plates which are disposed on opposite sides of one side wall of the buffer structure and are adapted to be clamped in direct contact with opposite sides of the adjacent rail by at least one clamping bolt which passes through one of the mutually spaced slots in said wall, the slots engaged by the bolts of the two-part clamps of each pair of clamps being substantially identical in length and the slots engaged by the bolts of the two-part clamps of each pair of clamps, except the first and upstream pair of clamps at the upstream end of the buffer structure, being greater in length than the slots engaged by the bolts of the two-part clamps of an adjacent upstream pair of clamps; whereby, on impact of a train with the buffer stop, the side walls of the buffer structure will move a first predetermined distance with respect to the permanent track so that the upstream end walls of the slots engaged by the bolts of the two-part clamps of the pair of clamps at said upstream end of the buffer structure will directly or indirectly abut said bolts to cause the side plates of said two-part clamps to slide with respect to the rails of the permanent track and to cause the energy of the train to be absorbed by frictional resistance between the relatively sliding contacting surfaces of the rails and side plates of the clamps, and the side walls of the buffer structure will move at least one further predetermined distance with respect to the permanent track, the or each further predetermined distance being of a greater length than the preceding predetermined distance, so that the upstream end walls of the slots engaged by the bolts of the two-part clamps of the or each succeeding pair of clamps will directly or indirectly abut said bolts to cause the side plates of said succeeding pair of clamps to slide with respect to the rails of the permanent track and to cause further energy of the train to be absorbed by frictional resistance between the relatively moving contacting surfaces of the rails and side plates of said succeeding pair of clamps in addition to that being absorbed by the frictional resistance between the relatively moving contacting surfaces of the rails and side plates of the or each preceding pair of clamps.
Preferably, each of the slots in each side wall of the buffer structure through which a clamping bolt passes is of such a length that, when the buffer stop is initially installed and before impact by a train, each bolt is in direct or indirect contact with the downstream end of the slot in which it is engaged. By virtue of this arrangement, after a train has made impact with the buffer stop and has been withdrawn, the buffer stop can be readily re-installed in its original position by loosening the clamping bolts, moving the buffer structure with respect to the permanent track until the bolts directly or indirectly abut the downstream end walls of the slots in which they are engaged, and then tightening the bolts, the buffer stop thereby automatically being re-installed in its correct position.
Each two-part clamp of each pair of clamps for detachably securing the side walls of the buffer structure to the rails of the permanent track may have a single clamping bolt passing through one of the slots in the adjacent side wall of the buffer structure but, preferably, each two-part clamp has a plurality of bolts mutually spaced along the length of the clamp and passing through a like plurality of mutually spaced slots in the side wall of the structure, each of the same length as one another, so that, when impact of a train with the buffer stop occurs and the side walls of the buffer structure move with respect to the permanent track, the upstream end walls of said plurality of slots abut the bolts passing therethrough simultaneously.
Preferably, at least one of the side plates of each two-part clamp of each pair of clamps has at least one transversely extending lug which passes through a slot in the associated side wall of the buffer structure and engages with the other side plate of said clamp and said clamping bolt passes through a transversely extending bore in said lug so that, when the side walls of the buffer structure move with respect to the permanent track when a train makes impact with the buffer stop, the upstream ends of said slots in the side walls will make direct contact with the transversely extending lugs of the clamps through which the clamping bolts pass. The or each transversely extending lug of each two part clamp of each pair of clamps preferably is of substantially circular cross-section and, in this case, preferably the upstream end wall of the slot through which the lug passes is of corresponding substantially semi-circular shape, thereby providing efficient means of resisting the applied loads.
In a preferred embodiment, each side plate of each two-part clamp of each pair of clamps has at least one transversely extending lug of substantially semi-circular cross-section which passes through a slot in the associated side wall of the buffer structure and co-operates with the semi-circular lug of the other side plate of the clamp to form a two-part lug of substantially circular cross-section. Preferably, the abutting diametrical faces of the lugs of semi-circular shape lie in a plane that will be approximately parallel to the plane containing the uppermost surfaces of the rails of the permanent track.
The axis of the transversely extending bore in the or each lug through which the clamping bolt passes may be co-linear with the axis of the lug but, to enhance clamping of the side plates of the clamp to the adjacent rail of the permanent track, preferably the axis of the transversely extending bore through the or each lug is inclined at an acute angle to the axis of the lug and substantially parallel to the preferred direction of the force to be imparted on the side plates to clamp them to the rail.
In addition to the advantages hereinbefore described, the improved buffer stop has the important advantage that it can be readily adapted to accommodate the impact of a train of any speed and load within wide limited ranges of speed and load by the provision of an appropriate number of pairs of two-part clamps. Furthermore, the buffer structure can be readily modified to accommodate any section of rail by use of side plates of appropriate shapes. Moreover, installation and re-positioning of the buffer structure can be readily effected because the two-part clamps are secured to and carried by the side walls of the buffer structure.